Materials Science
Finetuning-Free Diffusion Model with Adaptive Constraint Guidance for Inorganic Crystal Structure Generation
Auguste de Lambilly, Vladimir Baturin, David Portehault et al. (+4 more)
Generative
diffusion models have emerged as powerful tools for the discovery of inorganic
crystal structures, yet steering their sampling process toward user-defined physical and chemical objectives remains challenging. We present a computational framework that integrates adaptive constraint guidance into a pre-trained
crystal diffusion model, enabling the generation of candidate structures that satisfy targeted structural and chemical requirements without model retraining. The approach incorporates differentiable constraint functions directly during sampling, providing an interpretable mechanism for expert-driven exploration of the
crystal structure space. To assess the reliability of generated candidates, we introduce a multi-stage validation workflow combining descriptor-based analysis, duplicate removal, comparison with reference
crystal databases, graph neural network energy prediction, and thermodynamic stability evaluation through convex-hull analysis. The framework is applied to several classes of inorganic compounds and to constraints involving atomic volume, local coordination environments, and near-neighbor structural motifs. Results demonstrate that adaptive guidance effectively redirects the sampling distribution toward structures exhibiting the desired characteristics while preserving chemical plausibility. Subsequent validation reveals which generated candidates remain viable after energetic and thermodynamic screening. The proposed methodology provides a practical and transparent strategy for incorporating expert knowledge into
crystal generative models and establishes a general computational framework for constrained materials discovery.
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All authors Auguste de Lambilly, Vladimir Baturin, David Portehault, Guillaume Lambard, Nataliya Sokolovska, Florence d'Alché-Buc, Jean-Claude Crivello
Materials Science
Uncovering the role of ionic doping in hydroxyapatite: The building blocks of tooth enamel and bones
Mahdi Tavakol, Jinke Chang, Cyril Besnard et al. (+4 more)
Hydroxyapatite (HAp) is the primary mineral component of various mineralized tissues in the human body, including bone and teeth, where it performs critical roles of structural support and load transmission. In the context of dental health, the two most crucial properties of HAp are mechanical stability, which ensures resistance to forces, and chemical stability, which preserves surface integrity in acidic environments. During early stages of human
evolution, e.g. when teeth were used to crush uncooked food, mechanical stability was of paramount importance. However, with changes in diet and lifestyle, the principal origins of tooth damage and loss shifted towards bacterially mediated chemical attack, known as tooth decay, or caries. To enhance the chemical stability, ion doping has emerged as a particularly significant approach, and it lies at the focus of the present study. A Molecular Dynamics (MD) framework was developed to investigate the effects of ion doping on the chemical and mechanical stability of HAp and to identify optimal doping candidates. The framework combines conventional MD with Steered Molecular Dynamics (SMD), Thermodynamic Integration (TI) and uniaxial compression test simulations to provide comprehensive insights into the doping process. The findings revealed surface atoms as the most viable candidates for doping, as demonstrated by SMD and conventional MD simulations. Notably, TI calculations have identified magnesium ions as a better candidate among the ions considered here for enhancing the chemical stability of HAp. The results presented in this study offer valuable guidelines for synthesizing HAp-based substituent materials with properties tailored to meet the demands of modern dental applications such as implant coatings, enamel remineralization
agents and restorative materials.
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All authors Mahdi Tavakol, Jinke Chang, Cyril Besnard, Gabriel Landini, Richard M. Shelton, Jin-Chong Tan, Alexander M. Korsunsky
Materials Science
X-ray Absorption and Resonant X-ray Emission at the Carbon Edge of Li$_2$CO$_3$
John Vinson, Terrence Jach, Rainer Unterumsberger et al. (+2 more)
While highly successful, density functional theory is known to have limitations owing to its neglect of many-body electron-electron interactions. This neglect leads to errors in the single-particle energies, leading to underestimated band gaps and band widths as well as errors in band
alignment at interfaces. Many-body perturbation theory, in the form of the $GW$ self-energy correction, has been widely used to improve upon these short-comings. Though less well studied, the same $GW$ method is also able to predict the finite quasiparticle lifetime that is seen to cause anomalous broadening in the lowest-lying lines of valence emission spectra. Using near-edge x-ray absorption and emission, we probe the electronic structure of Li$_2$CO$_3$. Our measurements are compared to first-principles calculations, including $GW$ self-energy corrections to the single-particle energies and excitonic effects from the Bethe-Salpeter equation.
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All authors John Vinson, Terrence Jach, Rainer Unterumsberger, Michael A. Woodcox, Burkhard Beckhoff
Materials Science · Cross-listed from cond-mat.stat-mech
Global Oscillations in Depinning Models with Aging
F. V. Pereyra Aponte and E. A. Jagla
We propose a model that extends the standard depinning paradigm by incorporating an aging mechanism into the local pinning force. This favors oscillations between a stuck state of large pinning, and a slipping state of smaller pinning. We show that for mean field interactions between sites this mechanism can lead to the appearance of “king avalanches" and global instabilities, producing a global oscillatory stick-slip stress regime. We construct the phase diagram for this mean field case and identify regions of smooth dynamics, pure stick-slip, and bistability. Crucially, when considering two-dimensional systems with short-range interactions we find that states of global stress oscillation persist, but in contrast to the mean field case, no system-size avalanches appear. Instead, we observe alternating temporal intervals of larger and lower avalanche activity that correlate with the stress oscillations.
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Materials Science · Cross-listed from physics.ed-ph
Building an Affordable Self-Driving Lab: Practical Machine Learning Experiments for Physics Education Using Internet-of-Things
Yang Liu, Qianjie Lei, Xiaolong He et al. (+9 more)
Machine learning (ML) is transforming modern physics research, but practical, hands-on experience with ML techniques remains limited due to cost and complexity barriers. To address this gap, we introduce an affordable, autonomous, Internet-of-Things (IoT)-enabled experimental platform designed specifically for applied physics education. Utilizing an Arduino microcontroller, a customizable multi-wavelength light emitting diode (LED) array, and photosensors, our setup generates diverse, real-time optical
datasets ideal for training and evaluating foundational ML
algorithms, including traversal methods,
Bayesian inference, and deep learning. The platform facilitates a closed-loop, self-driving experimental workflow, encompassing automated data collection, preprocessing, model training, and validation. Through systematic performance comparisons, we demonstrate the superior ability of deep learning to capture complex nonlinear relationships compared to traversal and
Bayesian methods. At approximately $60, this open-source IoT platform provides an accessible, practical pathway for students to master advanced ML concepts, promoting deeper conceptual insights and essential technical skills required for the next generation of physicists and engineers.
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All authors Yang Liu, Qianjie Lei, Xiaolong He, Yizhe Xue, Kexin He, Haitao Yang, Yong Wang, Xian Zhang, Li Yang, Yichun Zhou, Ruiqi Hu, Yong Xie
Materials Science
Evidence for Umklapp electron scattering emission from metal photocathodes
I-J. Shan, L.A. Angeloni and W. Andreas Schroeder
Comparison of the measured spectral emission properties of single-
crystal Cu(001) and W(111) photocathodes to established photoemission theories reveal evidence for an additional one
photon emission process predominantly affecting electron emission near and below the photoemission threshold. This additional photoemission process is postulated to be due to a momentum-resonant Franck-Condon mechanism mediated by inelastic Umklapp electron scattering. An initial first-principles simulation of this emission process (involving the electron thermal effective mass, the inelastic electron mean free path at the
vacuum level, and the number of
Fermi surfaces in the metal), when combined with a direct one-step band emission model, is consistent with the measured spectral dependencies of both the
quantum efficiency and mean transverse energy of electron photoemission from the two single-
crystal metal photocathodes.
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Materials Science · Cross-listed from cond-mat.mes-hall
A. Shubnic, I. Chestnov, I. Lobanov et al. (+3 more)
We study the coupling between
spin excitations and acoustic waves in
bilayers of CrSBr, an ambiently stable 2D
magnetic material. We demonstrate that a strong dependence of inter-layer exchange coupling on strain makes possible the resonant generation of
magnons by an acoustic wave. It is shown that the parameters of the generation, in particular the resonant frequency, can be tuned by an external
magnetic field, which makes CrSBr a promising platform for spintronics applications.
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All authors A. Shubnic, I. Chestnov, I. Lobanov, V. Uzdin, I. Iorsh, I. A. Shelykh
Materials Science
Order-disorder transition and Na-ion redistribution in NASICON-type Na$_3$FeCr(PO$_4$)$_3$
Madhav Sharma, Archna Sagdeo and Rajendra S. Dhaka
We report the temperature-dependent synchrotron based X-ray diffraction analysis of NASICON type Na$_3$FeCr(PO$_4$)$_3$ sample, which undergoes a
symmetry-lowering structural transition from a monoclinic ($C2/c$) phase with long-range Na-vacancy order to a rhombohedral ($R\bar{3}c$) phase with statistical disordered Na ions. The [FeCr(PO$_4$)$_3$] polyanionic framework remains essentially unchanged, confirming that the transition is governed by redistribution of the Na sublattice rather than by reconstruction of the host framework. The structural
evolution is accompanied by a discontinuous increase in the $c$-axis and the unit-
cell volume, reflecting the progressive depopulation of the Na(1) sites and transfer of Na ions toward the Na(2) sublattice. The temperature dependence of superstructure intensity found to deviate from mean-field critical behavior, instead, the experimental
evolution is accurately captured by a sigmoidal phase-fraction model. The calorimetric measurements show that the enthalpy change for the first transition around 350~K is significantly larger than that of the anomaly around 445 K, indicating the dominant configurational rearrangement of Na ions occurs within the lower-temperature interval. Overall, the diffraction and calorimetric results demonstrate that Na ordering proceeds through an order-disorder transition involving intermediate Na configurations and a finite coexisting regime. The quantitative correlation between Na-vacancy ordering,
lattice strain, and
symmetry lowering reveals the central role of configurational interactions within the Na conduction channels in governing the phase stability of NASICON-type materials.
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Materials Science
All optical ultrafast pure spin current in the altermagnet Cr$_2$SO
Deepika Gill, Ruikai Wu, Peter Elliott et al. (+2 more)
All-optical generation of pure
spin current – the flow of
spin in the absence of a corresponding charge flow – relies on a
symmetry based compensation of valley charge. The 2d $d$-wave altermagnets, ideal spintronics materials due to a very low
spin-orbit coupling, possess a
magnetic point group and highly anisotropic valley
manifolds that would appear to preclude such current compensation, excluding them as materials for the ultrafast generation of pure
spin current. Here we show that infra-red valley excitation combined with a THz pulse envelope allows the generation of large and nearly 100% pure
spin currents in the altermagnet Cr$_2$SO. Our approach is based on a valley selection rule coupling linearly polarized light to
spin opposite valleys, along with the intrinsic momentum shift that a co-occurring THz pulse imbues a valley
spin excitation with. These results thus provide a practical and all-optical route to the generation of pure
spin current in $d$-wave 2d altermagnets, opening a route to lightwave control of
spin in an environment with very low intrinsic
spin mixing.
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All authors Deepika Gill, Ruikai Wu, Peter Elliott, Sangeeta Sharma, Sam Shallcross
Materials Science
Piezomagnetic Switching of Nonvolatile Antiferromagnetic States
Xilai Bao, Oleksandr V. Pylypovskyi, Huali Yang et al. (+17 more)
Prospective spintronic
memory and logic devices will benefit from the negligible stray field and ultrafast
magnetic dynamics inherent to antiferromagnets [1]. However, realizing isothermal, nonvolatile, and deterministic switching of
antiferromagnetic states remains a key challenge [2, 3]. Here, we propose a piezomagnetic writing scheme in triangular Mn3Ir-based
memory cells, with readout achieved via the exchange bias effect. Our approach enables deterministic and nonvolatile switching of the
antiferromagnetic states, which exhibit exceptional robustness against external perturbations. The switching mechanism is ascribed to piezomagnetic effect of Mn3Ir combined with the interfacial Dzyaloshinskii-Moriya interaction at the antiferromagnet-ferromagnet interface. This scheme overcomes the speed limitations imposed by conventional isothermal methods based on isothermal crystallization mechanism [4]. Our findings highlight the potential of piezomagnetic effects in designing advanced spintronic devices, providing an efficient pathway for manipulating
antiferromagnetic states and developing energy-efficient
memory technology.
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All authors Xilai Bao, Oleksandr V. Pylypovskyi, Huali Yang, Yali Xie, Damien Faurie, Fatih Zighem, Sophie F. Weber, Jiabin Wang, Jiachen Liang, Hong Xu, Ruoan Zou, Huatao Jiang, Dong Han, Pavlo Makushko, Xiaotao Wang, Lin Guo, Proloy T. Das, Nicola A. Spaldin, Denys Makarov, Run-Wei Li
Materials Science
Exact demagnetisation field for periodic one-dimensional array of rectangular prisms
Frederik Laust Durhuus, Andrea Roberto Insinga and Rasmus Bjørk
The
magnetic field from a uniformly magnetised, rectangular prism is known exactly, which is the basis for a large number of micromagnetic simulations. Here we derive an analytical solution for the field from a periodically repeating infinite array of prisms aligned end-to-end, which becomes exact on the center axis in the limit of infinitesimally thin prisms. Using the same method we derive the on-axis field for a one-dimensional array of point dipoles. We validate the obtained results numerically and furthermore compare with the common macrogeometry approach and more recent uniform magnetisation method, demonstrating an excellent convergence rate for the novel method.
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Materials Science
Two-Dimensional Ferromagnetism in Monolayers of MnSi
Yuan Fang, Yang Liu, Dmitry V. Averyanov et al. (+6 more)
2D ferromagnets offer valuable insights into the fundamentals of magnetism and stimulate the progress of ultracompact spintronics. The demand for seamless integration of the materials with the Si technology, particularly helpful to their applications in nanoelectronics, draws
attention to 2D
magnetic silicides. MnSi is a prominent silicide hosting
magnetic phases with unconventional properties; however, little is known about
magnetic states of MnSi at the 2D limit. Here, we explore the magnetism of ultrathin films of MnSi on silicon, down to a single monolayer. Angle-resolved photoemission spectra suggest exchange splitting of MnSi bands. Magnetization measurements confirm that the
ferromagnetic state in MnSi is rather robust with respect to the number of monolayers. Thick metallic films demonstrate the anomalous
Hall effect and negative magnetoresistance; however, as the number of monolayers drops below 3, MnSi becomes an
insulator. Most importantly, the ferromagnetism of ultrathin MnSi films acquires a 2D character, as its effective Curie temperature depends on weak
magnetic fields. The present study establishes MnSi monolayers as 2D ferromagnets that can find potential applications in silicon-based spintronics.
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All authors Yuan Fang, Yang Liu, Dmitry V. Averyanov, Ivan S. Sokolov, Alexander N. Taldenkov, Oleg E. Parfenov, Oleg A. Kondratev, Andrey M. Tokmachev, Vyacheslav G. Storchak
Materials Science
Stress field modification near linear complexions increases the effective obstacle size and strengthening effect
Zhengyu Zhang, Daniel S. Gianola and Timothy J. Rupert
Linear complexions are stable defect states that form along dislocations and recent experiments have demonstrated strengthening effects exceeding classical precipitation hardening predictions, motivating a detailed study of nanoscale strengthening mechanisms. Here, molecular dynamics simulations in Al-Cu and Ni-Al face-centered cubic
alloys are used to demonstrate distinct plasticity mechanisms associated with linear complexions. Both nanoparticle array and platelet array complexions exhibit appreciable strengthening. In addition to direct interactions with the particles, stress field modification in nearby regions can restrict dislocation motion as well. Finally, the relative particle-dislocation orientation is found to have a large effect, with the strongest resistance observed when the dislocation stress field aligns with the original complexion nucleation condition. As a whole, these findings provide mechanistic insight into the strengthening observed experimentally and establish design principles for linear complexion-induced strengthening in structural
alloys.
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Materials Science
Topographic patterning in perovskite oxide membranes for local control of strain, nanomechanics and electronic structure
Marti Ramis, Markos Paradinas, Jose M. Caicedo et al. (+3 more)
Single-crystalline perovskite
oxide membranes provide a powerful platform to access physical properties that are inaccessible in bulk
crystals and substrate-clamped thin films. Within this context, the deliberate fabrication of tailored corrugations provides a reliable mean to impose local
curvature enabling deterministic modulation of functional properties. Here, we demonstrate controlled topographic patterning in (00l)-oriented La$_{0.7}$Sr$_{0.3}$MnO$_3$ (LSMO) membranes with thicknesses ranging from 4 to 100 nm where they spontaneously form sinusoidal wrinkles with thickness-dependent periodicity and amplitude. The wrinkle morphology directly modulates membrane stiffness and generates exceptionally large local strains exceeding 5% with strain gradients approaching $\sim$ 2.5 x 10$^{7}$ m$^{-1}$ in the thinnest membranes. These extreme deformations suppress antiferrodistortive octahedral rotations and stabilize polar distortions, evidencing a
curvature-driven
symmetry transformation. The surface potential variation reinforces the formation of wrinkled-induced polar patterns being strongly modulated with thickness. The variation of Mn oxidation state from $\sim$ 3.2+ to $\sim$ 2.85+ provides a direct chemical signature of a thickness-controlled electronic transition. These results demonstrate that corrugation-induced strain gradients in
oxide membranes with different thicknesses can drive coupled structural, nanomechanical and electronic transformations, offering a singular route to engineer their functional states for next-generation electronic devices.
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All authors Marti Ramis, Markos Paradinas, Jose M. Caicedo, Claudio Cazorla, Roger Guzman, Mariona Coll
Materials Science · Cross-listed from cond-mat.mes-hall
Third-order optical response in d-wave altermagnets: Analytical and numerical results from microscopic model
Shihao Zhang
Altermagnets represent a novel category of
magnetic materials characterized by zero net magnetization yet featuring
spin-split band structures, and they demonstrate distinctive orbital-
spin locking phenomena. Commencing from the minimal multi-orbital tight-binding
Hamiltonian of d-wave altermagnets, we conduct an analysis of the general formulas for the third-order injection and shift currents. These currents are solely determined by the
quantum metric and
quantum connection, being free from Berry
curvature contamination. In the ideal scenario where the $\delta$-bond hopping $V_\delta$ approaches zero ($V_\delta = 0$), we derive closed-form analytical solutions for the third-order photoconductivities. For the general situation with a finite value of $V_\delta$, we present a perturbative analytical solution within the limit of $V_\delta \ll V_\pi$, and this solution is verified through numerical calculations. Our research establishes a comprehensive theoretical description of the third-order optospintronic responses in d-wave altermagnets based on a microscopic model. Moreover, it offers a viable approach for the experimental observation of pure
quantum geometric effects.
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Materials Science · Cross-listed from physics.app-ph
Automated Design of Tubular Origami with Anisotropic Stiffness
Mingkai Zhang and Davood Farhadi
Thin sheets can be assembled into tubular origami structures that combine deployability with pronounced anisotropic stiffness, enabling applications ranging from robotics to deployable systems. However, most existing tubular origami designs remain limited to degree-four vertex
topologies and are characterized primarily in axial and radial loading modes, without a full assessment of anisotropic stiffness. Here, we present an automated design framework for tubular origami that jointly explores local vertex
topology through generalized degree-$n$ vertices and global tube
topology through the polygonal cross-section, for the systematic design and optimization of anisotropic stiffness. Using a calibrated bar-and-hinge model together with experimental validation, we quantify large-deformation stiffness responses in axial translation, in-plane translation, torsion about the tube axis, and rotation about in-plane axes, thereby characterizing the anisotropic stiffness of the tube across its compliant and constrained deformation modes. The resulting design-space exploration showed that the polygonal cross-sectional
topology is the primary factor governing the anisotropic stiffness. We further show that increasing the local vertex degree can improve global structural performance, particularly for tubes with a small number of cross-sectional vertices, demonstrating that higher local kinematic freedom does not necessarily compromise stiffness at the structural scale. Compared with a
benchmark design, the optimized architectures achieve more than 50 times higher constrained rotational stiffness. Together, these results highlight higher-degree vertices and polygonal cross-sectional
topology as powerful design variables for tailoring anisotropic stiffness in tubular origami.
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Materials Science
Angle dependent hysteretic magnetotransport in MnBi2Te4 nanoflakes
Tithiparna Das and Soumik Mukhopadhyay
Controlling
magnetic phases in two-dimensional systems, where charge transport is highly sensitive to real-space
spin inhomogeneities, is central to understanding emergent
magnetic states in reduced dimensions. In this context, thickness-dependent magnetotransport provides access to irreversible
magnetic processes that are not captured by reversible transport or bulk magnetization alone. Here we report an extensive study of hysteretic magnetoresistance in single-crystalline nanoscale thin flakes of the layered antiferromagnet MnBi2Te4. The multi-step hysteresis exhibits a pronounced non-monotonic dependence on thickness and displays nontrivial angular anisotropy. The transport signatures rule out surface-dominated magnetism and simple bulk metamagnetic transitions as the primary origin. We argue that the
magnetic irreversibility is possibly governed by domain wall pinning and de-pinning processes within a spatially non-uniform
magnetic landscape. These results suggest that reduced dimensionality is a key driver of
magnetic irreversibility in MnBi2Te4.
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Materials Science
Cs$_4$Cr$_7$Te$_{10}$: Interwoven Reconstructed Archimedean and Kagome Lattices with a Possible Phase Transition near 130 K
Zhen Zhao, Ruwen Wang, Hua Zhang et al. (+12 more)
Chromium-based materials with complex
lattice geometries provide an important platform for investigating correlated electronic and
magnetic states. However, Cr-based compounds with unusual
crystal geometries are still rarely reported. Here, we report a new Cr-based compound, Cs$_4$Cr$_7$Te$_{10}$, featuring interwoven Cr and Te sublattices that can be viewed as reconstructed networks derived from Archimedean (3.4.6.4) tiling and the kagome
lattice, respectively. Transport measurements reveal the semiconducting nature in Cs$_4$Cr$_7$Te$_{10}$. Magnetization measurements show a weak anisotropy between H//b and H//ac planes, and uncover an anomaly near 130 K that is insensitive to the applied
magnetic fields. Specific-heat measurements further confirm this transition, indicating its bulk thermodynamic nature. The associated
entropy change is as small as 0.41 J mol^-1 K^-1, ruling out a structural phase transition and pointing to a possible electronic and/or
magnetic phase transition. These results provide a new route for designing complex
crystal geometries and exploring their associated emergent phenomena.
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All authors Zhen Zhao, Ruwen Wang, Hua Zhang, Tong Liu, Haisen Liu, Guojing Hu, Ke Zhu, Senhao Lv, Gang Cao, Chenyu Bai, Hui Guo, Xiaoli Dong, Wu Zhou, Haitao Yang, Hong-Jun Gao
Materials Science · Cross-listed from cond-mat.str-el
Robust topological surface states in skyrmion-host magnets Eu(Ga,Al)4: evidence for dual topology
Yuki Arai, Kosuke Nakayama, Takemi Kato et al. (+10 more)
The interplay between real-space
topology such as
magnetic skyrmions and momentum-space
topology characterized by topological surface states (TSSs) is predicted to realize novel phenomena and functionalities, yet materials hosting both
topologies are scarce. Skyrmion-hosting helimagnet family EuGa$_2$Al$_2$ and EuAl$_4$ has been a
prime candidate for such a dual-
topology system, but conclusive evidence for its momentum-space
topology has remained elusive. We provide this evidence by directly observing TSSs that stem from bulk Dirac nodal lines using high-resolution angle-resolved photoemission spectroscopy. These TSSs are exceptionally robust against various perturbations such as a 2$\times$1 surface reconstruction, a chemical change in the termination of the
crystal surface, and the onset of helical
antiferromagnetic order. Crucially, below the Neel temperature, we observe replica bands driven by the
magnetic ordering. Moreover, we demonstrate clear surface-termination dependence of this magneto-topological coupling. Our findings establish Eu(Ga$_{1-x}$Al$_x$)$_4$ as a dual-
topology material and offer a rare platform to explore and control the interaction between the two fundamental topological realms.
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All authors Yuki Arai, Kosuke Nakayama, Takemi Kato, Tomonori Nakamura, Asuka Honma, Seigo Souma, Kenichi Ozawa, Kiyohisa Tanaka, Daisuke Shiga, Hiroshi Kumigashira, Yoshinori Okada, Kouji Segawa, Takafumi Sato
Materials Science · Cross-listed from cond-mat.str-el
Origin of multiple skyrmion phases in EuAl4
Y. Arai, K. Nakayama, A. Honma et al. (+6 more)
The Dzyaloshinskii-Moriya (DM) interaction has been considered essential for skyrmion formation, however, the discovery of skyrmion
lattices (SkLs) in nominally centrosymmetric materials where the DM interaction is forbidden, such as Eu(Ga$_{1-x}$Al$_x$)$_4$, has challenged this established view. Recent structural investigations of Eu(Ga$_{1-x}$Al$_x$)$_4$ have further complicated this issue by revealing that the charge-density wave breaks local
symmetry, theoretically allowing DM interaction. This raises a fundamental question: are the complex
magnetic phases driven by the DM interaction or by alternative mechanisms? Here, using soft-x-ray angle-resolved photoemission spectroscopy, we determine the three-dimensional bulk electronic structure of Eu(Ga$_{1-x}$Al$_x$)$_4$, and elucidate the electronic origins of its rich
magnetic orders. We directly observe an x-dependent Lifshitz transition leading to the emergence of a
Fermi-surface pocket. Importantly, multiple nesting vectors derived from this pocket match the
symmetries and periodicities of the multiple SkLs. Moreover, these nesting vectors can also account for other
magnetic orders, such as the zero-field helical magnetism, suggesting a common electronic origin of the complex
magnetic phases. These findings suggest that competing nesting-induced Ruderman-Kittel-Kasuya-Yosida interactions and their engineering can generate and control various SkLs and related topological
spin textures.
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All authors Y. Arai, K. Nakayama, A. Honma, S. Souma, D. Shiga, H. Kumigashira, T. Takahashi, K. Segawa, T. Sato
Materials Science
Role of diffusion-induced grain boundary migration during molten salt corrosion of a Ni-30Cr alloy
Konnor Walter, Jagadeesh Sure, Adrien Couet et al. (+1 more)
The response of Ni-Cr
alloys to exposure to molten chloride and fluoride salts is typically characterized by Cr dealloying with the formation of a Cr-depleted bi-continuous porous subsurface layer. The exact mechanism behind the loss of Cr over distances unattainable by
lattice diffusion alone is still debated. To address this question, two different surface finishes, namely electropolished and sanded, of a Ni-30Cr
alloy were exposed to LiCl-KCl-2wt% EuCl3 eutectic salt at 500 {\deg}C for 96 hours. In the absence of fast
diffusion pathways, dissolution occurred layer by layer and was kinetically controlled by Ni dissolution, as observed over the grain interiors of the electropolished sample. Grain boundaries were subject to
diffusion-induced grain boundary migration (DIGM), leading to the formation of pure Ni islands above grain boundaries. This overall behavior contrasted with the sanded surface response that was characterized by several micrometer deep interconnected porosity and complete Cr depletion. DIGM of the dense grain boundaries created by recrystallization of the sanded surface was responsible for the observed sub-surface microstructure. This work unequivocally establishes DIGM as a key mechanism in
alloy molten salt corrosion, and microstructure as a decisive contributor to an
alloy's corrosion response.
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All authors Konnor Walter, Jagadeesh Sure, Adrien Couet, Emmanuelle A. Marquis
Materials Science
Nonmonotonic Scaling of the Anomalous Hall Effect in a Bicollinear Antiferromagnet
Ruifeng Wang, Chi Fang, Ilya Kostanovski et al. (+5 more)
An anomalous
Hall effect (AHE) in
antiferromagnetic (AF) systems with no net magnetization is of considerable interest for both fundamental physics and spintronic applications. Of particular interest is the two-dimensional van der Waals antiferromagnet FeTe that has an unusual fully magnetically compensated bicollinear AF structure and exhibits pronounced Kondo interaction leading to strong band renormalization. Here, we investigate the AHE in epitaxial FeTe thin films grown by molecular beam epitaxy. A large anomalous
Hall conductivity is exhibited below the Neel temperature (T_N ~ 60 K) and, strikingly, becomes nonlinear at high fields within a narrow temperature window around 49 K, deviating from conventional AHE scaling behavior versus its longitudinal conductivity. Linear fits reveal a pronounced negative peak in the intercept, accompanied by a field-induced canted
magnetic moment. The AHE responses are related to the Berry
curvature derived from FeTe's topological band structure, highlighting the intricate interplay between
topology, magnetism, and electronic transport.
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All authors Ruifeng Wang, Chi Fang, Ilya Kostanovski, Ke Xiao, Felix Küster, Jenny Davern, Naoto Nagaosa, Stuart S. P. Parkin
Materials Science · Cross-listed from cond-mat.mes-hall
Remote Moiré Modulation of Decoupled Dirac Subsystems in Twisted Trilayer Graphene
Dohun Kim, Junsik Choe, Minseo Cho et al. (+4 more)
Moiré superlattices are generally assumed to act only at the interface where
lattice mismatch or twist occurs. Here, we study charge transport in large-angle helical twisted trilayer
graphene, where interlayer tunneling is strongly reduced. When only the top monolayer
graphene is aligned with hBN, the electronic response reorganizes into a moiré-modulated monolayer and a remaining twisted
bilayer graphene subsystem. Despite the absence of any explicit structural moiré in the twisted
bilayer, we observe satellite-like features in its electronic response that run parallel to the primary spectrum and are locked to the density scale of the hBN/
graphene moiré. These observations are consistent with a weak moiré-periodic electrostatic perturbation generated at the aligned interface and sensed by a spatially separated Dirac subsystem, even in the absence of coherent interlayer coupling.
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All authors Dohun Kim, Junsik Choe, Minseo Cho, Takashi Taniguchi, Kenji Watanabe, Gil Young Cho, Youngwook Kim